Conventionally, in the case of forming a permanent pattern such as solder resist, at the time of forming a photosensitive layer on an objective member, a coating film is formed and dried from a photosensitive composition in a liquid form by using a spin-coating method, a screen printing method and a spray printing method, or a method of applying and drying a photosensitive composition on a temporary support to obtain a laminate film having a photosensitive layer and transferring only the photosensitive layer onto a member by means of a vacuum laminator or a roll laminator. As for the method to form a permanent pattern such as solder resist, there is known, for example, a method where a photosensitive layer is formed by the method above on a substrate such as a silicon wafer for formation of a permanent pattern, a silicon wafer having wiring thereon, or a copper-lined laminate board, and the photosensitive layer of the laminate is exposed, then developed to form a pattern and subjected to a curing treatment or the like, thereby forming a permanent pattern.
This permanent pattern formation is also applied to a package substrate interposed between a semiconductor chip and a printed board. As for the package substrate, higher density packaging is recently demanded, and reduction in the wiring pitch, increase in the strength of a solder resist layer, enhancement of the insulating property, thin film formation and the like are proceeding. In turn, resistance to repeated heat/cold shocks (thermal cycle test resistance, TCT resistance) is more keenly demanded. Also, reduction in the via diameter and in view of mounting, a rectangular pattern profile are required.
Furthermore, the photosensitive composition for the formation of a permanent pattern represented by such a solder resist is demanded to ensure that even when a member having a permanent pattern is placed under high-temperature high-humidity conditions, deformation of the permanent pattern or separation of the permanent pattern from the base material does not occur. For example, when such a defect is generated in a solder resist, there arises a problem that a wiring covered with the solder resist develops a dendrite and adjacent wirings are electrically conducted unintentionally. Therefore, it is also important that the solder resist has excellent durability to high temperature and high humidity.
On the other hand, a solid-state imaging device (image sensor) used in cellular phones, digital cameras, digital videos, monitoring cameras and the like is a photoelectric conversion device having an integrated circuit formed using the production technique of a semiconductor device. In recent years, with reduction in size and weight of a cellular phone or a digital camera, the solid-state imaging device is required to be more downsized.
For downsizing the solid-state imaging device, a technique of applying a penetrating electrode or thinning a silicon wafer has been proposed (see, for example, JP-A-2009-194396 (the term “JP-A” as used herein means an “unexamined published Japanese patent application”)). Downsizing can be realized by polishing and thereby thinning the silicon wafer, but due to thinning of the silicon wafer, light at a wavelength of 800 nm or more is liable to be transmitted, though the effect of blocking light at 800 nm or less is maintained. A photodiode used in the solid-state imaging device reacts also to light at 800 to 1,200 nm, and transparency to light at 800 nm or more is found to cause a new problem that the pictorial quality is deteriorated.
The solid-state imaging device has a configuration that a color filter and a lens are provided adjacently to one side of a photodiode, an infrared cut filter is present in the vicinity of the color filter or lens to cut light at 800 to 1,200 nm, and a metal wiring, a solder resist and the like are present on the opposite side of the color filter. For example, the space between metal wirings is filled with a solder resist in many cases, but there is a problem that infrared light such as leakage light intruding into the inside of a cellular phone, a digital camera or the like cannot be cut by the solder resist. To cope with this problem, a technique of further providing an infrared-blocking layer on the outer side of the solder resist poor in the light-blocking effect for infrared light and thereby ensuring the infrared-blocking effect has been conventionally employed. However, a height difference due to wiring or the like is generally present on the solder resist and an infrared-blocking layer material can be hardly coated to a uniform thickness on a substrate surface having a height difference, which gives rise to a problem that if a thin portion exits, light is transmitted therethrough.
In order to provide an infrared-blocking layer only in a desired portion, the composition preferably exhibits photosensitivity and has a photolithography performance enabling patterning by exposure. The light-blocking photosensitive composition having a photolithography performance includes a black resist using carbon black employed for the formation of an LCD color filter. The carbon black has a high light-blocking effect in the visible region but exhibits a low light-blocking effect in the infrared region and in the case where such a black resist is applied as a solder resist, if carbon black is added in an amount large enough to ensure the required light-blocking effect in the infrared region, this causes a problem that the light-blocking effect in the visible region becomes excessively high, the exposure light at a shorter wavelength than the visible region, such as high-pressure mercury lamp, KrF and ArF, which is usually used for image formation, is also cut, failing in obtaining sufficient photo-curability, and an excellent pattern cannot be obtained even when passed through a development step using an alkali developer.
Also, at present, an infrared-blocking layer is separately provided after forming a solder resist by a coating method and therefore, in the solder resist formation and the infrared-blocking layer formation, steps such as coating, exposure, development and post-heating must be performed a plurality of times, which leads to a cumbersome process and a rise in the cost. Therefore, improvements are required.
For meeting the requirement, it has been attempted to impart a light-blocking effect to the solder resist itself and, for example, a black solder resist composition containing a black colorant, a colorant other than black, and a polyfunctional epoxy compound have been proposed (see, for example, JP-A-2008-257045). However, this composition is characterized in that the content of the black colorant is kept low by using a colorant other than black in combination, and is practically insufficient in terms of satisfying both light-blocking effect, particularly light-blocking effect in the infrared region, and pattern formability.